Making & fitting the braking system
The braking system is taken from the donor Sierra and modified to suit the different requirements of the Indy. The front calipers are reconditioned exchange units from Burton Power as the original donor items were unserviceable and new discs and pads have been fitted. The original rear brake drums have been cleaned and re-fitted with new wheel cyclinders and brake shoes.
The Indy chassis design features floor mounted pedals with the brake master cylinder mounted directly to the chassis bulkhead without a vacuum servo to assist braking. The general consensus of opinion appears to be that this style of car is light enough not to require assisted braking and having driven MK's original demonstrator Indy which featured unassisted braking I feel this is a perfectly good set-up. There is plenty of discussion on this topic on www.locostbuilders.co.uk.
The original master cylinder from the donor was in good condition so this was removed from the servo unit and fitted to the pre-cut location hole in the chassis bulkhead. Once this had been fitted the pivot position and length of the brake pedal to master cylinder pushrod could be established. Following advice from MK and other car builders I positioned the pivot point to achieve a 5:1 pedal ratio. This means the pedal will be relatively heavy to push, but should give effective braking action. I sourced and modofied an adjustable clevis and pushrod assembly from Merlin Motorsport, which will allow fine tuning of the brake pedal position for comfort and safety.
I have since got a book called "How to build and modify suspension and brakes" by Des Hammill, which contains has a wealth of very clearly presented info. on this type of activity - highly recommended!
Published by Veloce - ISBN 1903706734
The original Sierra braking system features a brake proportioning valve, which regulates the force applied to the rear brakes. This is necessary to prevent the rear wheels from locking up before the front under heavy braking, which would make the car difficult to control. The Sierra proportioning valve is a fixed device installed at a precise angle in relation to the vehicle to provide the best balance for normal road driving under a wide range of conditions. In order to build more flexibility into my braking system I chose to fit an adjustable valve, allowing me to fine tune the operation of the brakes for the prevailing conditions and weight of the car. I looked at several motorsport components (all of which are upwards of £80) before I found out about the adjustable device fitted as standard to early Fiat Unos. Armed with this knowledge and some tools I retrieved a suitable valve from the scrappy for £5 - bargain. In order to fit the Uno valve and achieve the adjustability I fabricated a metal bracket, with a screw and locknut arrangement. This was then fitted to the bulkhead of the chassis, above the master cylinder.
Next I sourced some flexible brake hoses to run between the front calipers/rear wheel cyclinders and the chassis. These are off the shelf Lucas parts, which means they are cheap and easy to replace. I fabricated some small metal brackets which are bolted/rivetted to the chassis to secure the hoses for connection to the fixed brake pipes. Fixed Copper brake pipes were formed by hand to run between the various components of the braking system - this is an enjoyable task and easier than I thought it would be. Once formed and flared the fixed Copper pipes are clipped to the chassis using plastic 'P' clips and rivets and 250mm (or less) intervals.
NB - A good quality set of pipe cutting and flaring tools are essential for this job, nothing less will do!
The master cylinder is a tandem design meaning that it effectively has 2 cylinders inline in a single housing. Their are seperate outlets for the left and right front brakes and a single outlet for the rear brakes. The front outlets are routed along the chassis in the engine bay and up to the flexible hose brackets for the front calipers. The rear outlet is routed via the proportioning valve and down the inside of the transmission tunnel. At the back of the chassis the rear brake pipe is split 3 ways using a 4 way brass union (1 in, 3 out) bolted to the chassis. This allows for 2 seperate brake lines to be routed to the rear flexible hose brackets for the rear wheel cylinders. The 3rd outlet of the union is used to fit a pressure sensitive brake switch, which will be used to control the brake lights.
The rear flexi hoses cannot be directly connected to the rear wheel cylinders due to the design of the rear suspension uprights. To get around this problem some short Copper brake pipes were formed to fit between the wheel cylinder and a fabricated metal bracket rivetted onto the upright. This allows the flexi hoses to be routed away from moving parts and without any unecessary kinks.
